1. Field of the Invention
This invention relates to a stent crimping device of the type that will enable the user to crimp a stent onto the distal end of a balloon catheter assembly, for example of the kind used in a typical percutaneous transluminal coronary angioplasty (PTCA) procedure.
2. Description of the Related Art
In a typical PTCA procedure, for compressing lesion plaque against the artery wall to dilate the artery lumen, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end is in the ostium. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient's coronary vasculature, and the dilatation catheter is advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, a flexible, expandable, preformed balloon is inflated to a predetermined size at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile, so that the dilatation catheter can be withdrawn from the patient's vasculature and blood flow resumed through the dilated artery. While this procedure is typical, it is not the only method used in angioplasty. Other methods to open a vessel are known, such as atherectomies and plaque dissolving drugs.
In angioplasty procedures of the kind referenced above, a restenosis of the artery may develop over several months, which may require another angioplasty procedure, a surgical bypass operation, or some method of repairing or strengthening the area. To reduce the chance of the development of restenosis and strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, typically called a stent. A stent is a device used to hold tissue in place in a vessel or to provide a support for a vessel to hold it open so that blood flows freely. A variety of devices are known in the art for use as stents, including expandable tubular members, in a variety of patterns, that are able to be crimped onto a balloon catheter, and expanded after being positioned intraluminally on the balloon catheter, and that retain their expanded form. Typically, the stent is loaded and crimped onto the balloon portion of the catheter, and advanced to a location inside the artery at the lesion. The stent is then expanded to a larger diameter, by the balloon portion of the catheter, to implant the stent in the artery at the lesion. Examples of stents and delivery catheters as described are disclosed in more detail in U.S. Pat. No. 5,102,417 (Palmaz), U.S. Pat. No. 5,569,295 (Lam), and U.S. Pat. No. 5,514,154 (Lau et al.).
However, if the stent is not effectively crimped onto the catheter balloon portion, when the catheter is advanced in the patient's vasculature the stent may move or even slide off the catheter balloon portion in the body lumen or coronary artery prior to expansion, and may block the flow of blood, requiring procedures to remove the stent.
In procedures where the stent is placed over the balloon portion of the catheter, the stent must be crimped onto the balloon portion to prevent the stent from sliding off the catheter when the catheter is advanced in the patient's vasculature. In the past this crimping was often done by hand, which does not provide optimum results due to the uneven force being applied, resulting in non-uniform crimps. In addition, it was difficult to judge when a uniform and reliable crimp had been applied. The prior art tools and methods have not been entirely adequate in achieving a uniform crimp. Stent designs generally are based on a uniform metal-to-artery ratio for the highest success rate, thus a non-uniformly crimped stent may result in an unevenly expanded stent in the vessel or artery, which is undesirable.